Navigation system using spreading codes based on pseudo-random noise sequences

1. A receiver for use in a navigation system comprising multiple transmitters, each transmitter transmitting a positioning signal comprising a pseudo-random noise (PRN) sequence corresponding to the respective transmitter, the receiver comprising: a code module for supplying multiple PRN sequences corresponding to the respective multiple transmitters, wherein the code module includes memory for storing the multiple PRN sequences or digital logic circuitry for generating the multiple PRN sequences on the fly, wherein said multiple PRN sequences are based on a single Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence u SLCE that provides a family of N/2 PRN sequences where N is the length of each PRN sequence in the family, each of said PRN sequences in the family, denoted u i , satisfying the equation: u i =u SLCE ⊕T i u SLCE , where ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips; and a correlator for correlating the multiple PRN sequences supplied by the code module with an incoming signal to detect positioning signals from respective transmitters, wherein the multiple pseudo-random noise (PRN) sequences supplied by the code module comprise a subset of the N/2 pseudo-random noise (PRN) sequences in the family, said subset being selected by an optimization procedure to provide good correlation properties for odd correlation, wherein odd correlation represents a change in polarity of the PRN sequence being correlated.

2. The receiver of claim 1 , wherein multiple PRN sequences have an even length, equal to a prime number minus 1.

3. The receiver of claim 1 or 2 , wherein none of the multiple PRN sequences has a balance greater than four.

4. The receiver of claim 3 , wherein all the multiple PRN sequences have a balance of zero.

5. The receiver of claim 1 , wherein u SLCE is derived from a primitive root element of a prime number p, and the maximum correlation magnitude for said multiple PRN sequences is given by 4+2┌√{square root over (N)}┐, where N=p−1.

6. The receiver claim 1 , wherein u SLCE is derived from a primitive root element of a prime number p, and the maximum correlation magnitude for said multiple PRN sequences is given by 12+2┌√{square root over (N)}┐, where N=p−1.

7. A method of operating a receiver for use in a navigation system comprising multiple transmitters, each transmitter transmitting a positioning signal comprising a pseudo-random noise (PRN) sequence corresponding to the respective transmitter, the method comprising: receiving an incoming signal at the receiver; supplying, form a code module, multiple PRN sequences corresponding to the positioning signals of the respective multiple transmitters, wherein the code modules includes memory for storing the multiple PRN sequences or digital logic circuitry for generating the multiple PRN sequences on the fly, wherein said multiple PRN sequences are based on a single Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence u SLCE that provides a family of N/2 PRN sequences, where N is the length of each PRN sequence in the family, each of said PRN sequences in the family, denoted u i , satisfying the equation: u i =u SLCE ⊕T i u SLCE , where ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips; and correlating the incoming signal against multiple PRN sequences supplied by the code module with the incoming signal to detect positioning signals from respective transmitters; wherein the multiple pseudo-random noise (PRN) sequences comprise a subset of the N/2 pseudo-random noise(PRN) sequences selected by an optimization procedure to provide good correlation properties for odd correlation, wherein off correlation represents a change in polarity of the PRN sequence being correlated.

8. A navigation system comprising multiple transmitters, each transmitter transmitting a positioning signal comprising a pseudo-random noise (PRN) sequence corresponding to the respective transmitter, each transmitter comprising: a code module for supplying a PRN sequence corresponding to the positioning signal of said transmitter, wherein the code module includes memory for storing the PRN sequence or digital logic circuitry for generating the PRN sequence on the fly, wherein said PRN sequence for each respective transmitter is generated according to: u i =u SLCE ⊕T i u SLCE , where u SLCE is a single Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence, ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips, and different transmitters have a different respective PRN sequence by selecting a different value of i, and wherein the generative sequence provides a family of N/2 pseudo-random noise (PRN) sequences, where N is the length of each PRN sequence in the family; and a transmitter module for transmitting the PRN sequence supplied by the code module, wherein the pseudo-random noise (PRN) sequences corresponding to the multiple transmitters comprise a subset of the N/2 pseudo-random noise (PRN) sequences selected by an optimization procedure to provide good correlation properties for odd correlation, wherein odd correlation represents a change in polarity of the PRN sequence being correlated.

9. The navigation system of claim 8 , wherein at least one of the transmitters comprises a satellite.

10. The navigation system of claim 8 , wherein at least one of the transmitters comprises a pseudolite.

11. A method of operating a navigation system comprising multiple transmitters, each transmitter transmitting a positioning signal comprising a pseudo-random noise (PRN) sequence corresponding to the respective transmitter, the method comprising each transmitter: supplying a PRN sequence from a code module to a transmitter module in said transmitter, the PRN sequence corresponding to the positioning signal of said transmitter, wherein the code module includes memory for storing the PRN sequence or digital logic circuitry for generating the PRN sequence on the fly, wherein said PRN sequence for each respective transmitter is generated according to: u i =u SLCE ⊕T i u SLCE , where u SLCE is a single Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence, ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips, and different transmitters have a different respective PRN sequence by selecting a different value of i, and wherein the generative sequence provides a family of N/2 pseudo-random noise (PRN) sequences, where N is the length of each PRN sequence in the family; and transmitting the PRN sequence supplied by the code module from the transmitter module; wherein the multiple pseudo-random noise (PRN) sequences comprise a subset of the N/2 pseudo-random noise (PRN) sequences selected by an optimization procedure to provide good correlation properties for odd correlation, wherein odd correlation represents a change in polarity of the PRN sequence being correlated.

12. A method of generating a set of pseudo-random noise (PRN) sequences for use in a navigation system comprising multiple transmitters, each transmitter transmitting a positioning signal corresponding to the respective transmitter, wherein each positioning signal comprises one of the set of pseudo-random noise (PRN) sequences, the method comprising: providing a Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence, u SLCE ; generating each PRN sequence in said set of PRN sequences according to: u i =u SLCE ⊕T i u SLCE , where ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips, wherein the generative sequence provides a family of N/2 pseudo-random noise (PRN)sequences, where N is the length of each pseudo-random noise (PRN)sequence in the family; and selecting the set of multiple pseudo-random noise (PRN)sequences as a subset of the family of N/2 pseudo-random noise (PRN)sequences using an optimization procedure to provide good correlation properties for odd correlation, wherein odd correlation represents a change in polarity of the PRN sequence being correlated.

13. The method of claim 12 , further comprising selecting the set of PRN sequences such that each PRN sequence has a balance of zero.

14. A communication system comprising multiple transmitters and receivers, in which multiple transmissions are performed in parallel from the transmitters to the receivers, each of said multiple transmissions being encoded using a spreading code comprising one of a set of pseudo-random noise (PRN) sequences, wherein each PRN sequence in said set of PRN sequences is particular to a respective transmitter and is specified by: u i =u SLCE ⊕T i u SLCE , where u SLCE denotes a Sidelnikov/Lempel/Cohn/Eastman (SLCE) generative sequence, ⊕ indicates element by element binary XOR addition, and T i indicates a cyclic shift of i chips, wherein the generative sequence provides a family of N/2 pseudo-random noise (PRN)sequences, where N is the length of each pseudo-random noise (PRN)sequence in the family; wherein the set of multiple pseudo-random noise (PRN)sequences comprise a subset of the N/2 pseudo-random noise (PRN)sequences in the family, the subset being selected by an optimization procedure to provide good correlation properties for odd correlation, wherein odd correlation represents a change in polarity of the PRN sequence being correlated; and wherein each receiver stores or generates using digital logic circuitry each of the PRN sequences in said set of PRN sequences for identifying transmissions from each respective transmitter.